Mono cameras do not have a uniform sensitivity across the color spectrum. See if you can find a spectral sensitivity curve for your camera and you will see the difference.
For bayer matrix cameras the extra green pixels translates into better green resolution not increased sensitivity. The sensitivity is a function of each pixel and does not increase with more pixels. However, like mono cameras the pixels may be more sensitive to green.
PixInsight is specifically designed for astrophotography processing and does a great job. With PixInsight you can do all your processing with one tool, and the price is quite reasonable. The only downsides are that it takes some effort to learn and it does not have painting tools like Photoshop.